The present invention relates to an operator presence sensing system that permits a seat to be mounted on adjustable seat rails for ease of positioning in fore and aft direction, while providing a signal indicating when the seat is supporting more than a desired amount of weight.
Vehicle seat switches have been used in the past for determining the presence of an operator, so that various interlocks can be actuated when the operator is not present on the seat. Improved reliability of these systems is sought, particularly when the vehicle is used where dirt and other foreign objects are present.
It is further desirable to have the seat adjustable in the same manner that they presently are adjustable, while maintaining the reliability of the sensing system.
U.S. Pat. No. 5,124,512 shows a vehicle seat switch which utilizes a base panel that moves up and down and actuates a spring loaded mechanical switch at the forward edge of the unit. A wire type spring or spring frame is utilized and a base plate acts against the spring frames to cause actuation of an existing switch, such as a microswitch. In a second form of the invention a switch actuator comprising a bowed leaf spring that is straightened under load actuates a mechanical switch.
Adjusting the seat utilizing this type of arrangement is not disclosed in the patent, and it appears that making the seat adjustable involves additional structural components, and would complicate the overall operation of the seat.
U.S. Pat. No. 4,075,443 illustrates a type of switching mechanism that operates on the springs within a seat cushion. This permits the seat to be mounted in normal manner on adjustable rails that permit sliding of the seat, but the positioning of a switch for accurate operation in relation to the seat springs is difficult to precisely maintain, and it appears from the construction that adjustment would be difficult.
A sensing apparatus that has switches along the lateral side of the seat is shown in U.S. Pat. No. 4,361,741. The operation relies upon a pivoting plate in one form of the invention, and in another form of the invention depends on deflection of the seat spring itself for actuation. A feature of this patent is to control the force that is applied to the mechanical switch to avoid damage to the switch itself.